The invention relates generally to methods and apparatus for printing and recording text, indicia, images, and other information on a medium such as paper, for example. More particularly, the invention relates to print head motion control for a printing apparatus comprising a housing which is manually positioned adjacent to a surface of the print medium, said housing remaining stationary with respect to the medium while printing is accomplished by raster scanning of a print head over multiple paths within the housing.
Two distinct methods of generating images for display or printing are well known. The term raster scanning refers generally to the process of generating an image as a series of rows and columns of pixels, or individual image elements, as is familiar from its use in generating television pictures, for example, or as is used in dot matrix or ink jet printers as are well known. This contrasts with the generation of an image by vectors, also known as vector graphics, where an image is generated by drawing lines comprising the image one line at a time, from point to point, as would be done manually with a pencil, for example, or as may be done by a plotter as is well known.
Various types of printing devices have been disclosed with the objective of printing on the surface of a medium external to a print apparatus held stationary on the medium. U.S. Pat. No. 4,089,262, awarded to Sopora, discloses a printing mechanism wherein the marking device xe2x80x9c . . . follows the contours of the characters to be printed . . .xe2x80x9d, hence it generates an image via the vector graphics method. This method inherently requires that the print head be movable in a multiplicity of directions such that characters can be drawn, and requires complex control mechanisms and algorithms.
Generally the raster scan method offers a number of advantages over the vector method of generating an image. The print head is scanned over the print area in an ordered, known manner, regardless of the content of the image. This simplifies control, and will in general result in faster printing than the vector method, where each and every line of the image must be individually drawn.
U.S. Pat. No. 5,634,730, awarded to the present applicant, Bobry, discloses a printing mechanism, as a portion of a printing apparatus, wherein a print head generates a raster scan image as a series of columns of pixels laid down as the print head moves on a single path over the surface of the print medium, as the head travels from a starting position of the path to an ending position of the path; and/or on the return pass of the head over the same path, as the head is returned from the ending position to the starting position. This single path raster scan printing mechanism offers the advantages of fast printing and simple control, but is limited in the size of the image which can be printed. One dimension of the image is limited to the image swath of the print head.
European patent application number EP 0 449 157 A1, filed by Damiano; European patent application number EP 0 598 2251 A1, filed by Wolf; and U.S. Pat. No. 5,685,651, awarded to Hayman et al., all disclose printing mechanisms wherein a print head passes over the surface of the print medium on multiple paths so as to generate a raster scan image. Such multiple path raster scan printing mechanisms are advantageous in a number of applications because they allow the printing of larger images than the single path mechanism, albeit with a sacrifice in speed, but nonetheless at a much higher printing speed than allowed by the vector method.
It is desirable for a printer incorporating a multiple path raster scan printing mechanism to be interoperable with an external apparatus which provides the information to be printed, such as a personal computer, for example, via the use of a conventional printer interface as is well known. Preferably, the printer is operable with a personal computer through the use of the commands and physical connection means which have become widely used and well known for purposes of operating conventional desk top printers with personal computers. Such connection means include, for example, cable connections to parallel, serial, or USB computer ports; or wireless connections via optical (infra red) or radio frequency means as are well known.
It has been acknowledged in the prior art that such interoperability between a printer and a personal computer requires that the printer incorporate control circuitry which functions to communicate with the computer, and interpret the data and instructions received, as well as to command the printer""s print head and movement drives to accomplish the desired printing function. It has not, however, been previously recognized that such control circuitry, when used in a printer incorporating a multiple path raster scan printing mechanism, must operate in a significantly different manner from that in a conventional desk top printer. To wit, the conventional desk top printer incorporates a first movement drive which moves the print head back and forth, or bidirectionally, across the surface of the print medium, and a second movement drive which advances the print medium with respect to the print head in one direction only, i.e. unidirectionally, whether such advance is a single line advance to allow for the printing of an additional line, or a multiple line advance, or form feed, for the purpose of readying the printer to print a new image, or to continue an image or print job on a subsequent page. The multiple path raster scan printers anticipated in the prior art likewise incorporate a first movement drive which moves the head bidirectionally, but unanticipated is the fact that the second movement drive must be bidirectional, not unidirectional. If a unidirectional drive were used, the printer mechanism would be advanced, printing one line at a time, until the second movement drive reached the end of its travel. At that point, with unidirectional drive capability only, printing would have to cease, there being no means to return the second movement drive to its starting position to print another image. Merely making the second movement drive bidirectional is insufficient, however, as control means must be provided within the printing device to carry out the reset operation autonomously upon completion of the print job, that is, without the receipt of additional instructions from the host computer.
Alternatively, means can be provided for the operator to manually reset the printer mechanism to its starting position prior to starting the next print job, or means can be provided to reset the printer mechanism using energy stored during the previous print job. As a further alternative, a new type of multiple path raster scan printer mechanism is disclosed in which the motion of the print head is inherently cyclical, even with the use of a unidirectional motor drive, with the result that the position of the print head at the end of a print job corresponds with the starting point of the next print job.
It is the objective of the present invention, therefore, to provide methods and apparatus for control of print head motion in a multiple path raster scan printer, including means for reset of the printer in preparation for a subsequent print job.
To the accomplishment of the foregoing objectives, the present invention contemplates, in one embodiment, a multiple path raster scan printer wherein a first movement drive comprises a bidirectional motor drive, and a second movement drive comprises a unidirectional motor drive in combination with means for an operator to manually restore said drive to a starting position after completion of a printing operation. A second embodiment contemplates a multiple path raster scan printer wherein a first movement drive comprises a bidirectional motor drive, and a second movement drive comprises a unidirectional motor drive in combination with means to restore said drive to a starting position after completion of a printing operation using energy stored, during said printing operation, in an element such as a spring. A third embodiment contemplates a multiple path raster scan printer wherein a first movement drive comprises a bidirectional motor drive, and a second movement drive comprises a bidirectional motor drive, and further comprises a controller such that said drives are electrically restored to a starting position after completion of a printing operation. A fourth embodiment contemplates a multiple path raster scan printer wherein a first movement drive comprises a bidirectional motor drive, and a second movement drive comprises a bidirectional motor drive, and further comprises a controller such that said drives are reversed after completion of a printing operation so that the position of the print head at the completion of the printing operation becomes the starting position for the next printing operation. A fifth embodiment contemplates a multiple path raster scan printer wherein a first movement drive comprises a bidirectional motor drive, and a second movement drive comprises a unidirectional motor drive coupled to a cyclically bidirectional drive mechanism.